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Introduction to Travel Demand Modeling
El Dorado County Public WorkshopJune 28, 2012
“essentially all models are wrong, but some are useful” -George E. P. Box
Agenda• Travel Demand Modeling
– Why update the EDC model? – Land Use Policy Programmatic Update– What is a travel demand model?– Micro vs Macro– Four Step Process– What the model can and can not do
• Land Use Forecasting– Achievable Development– 2035 Projections– 2035 Land Use Forecast
• Questions and Answers
Why update the EDC model?
• Latest model version developed in 1998
• New software packages are available• Planning horizon has changed• Development patterns have changed• Doesn’t maximize the use of GIS• Concern about output
Land Use Policy Programmatic Update
What is a travel demand model?
• Tool for understanding human behavior
• Forecasts trips onto transportation facilities
• Part of the planning process
The completely over‐simplified basics of travel demand modeling
• Assumptions– people + jobs = trips– trips = traffic volumes/riders
• Application– Forecast people + jobs 20‐30 years out– Estimate demand/test improvements/
• Primary use is to forecast future travel
The not‐so‐simplified flow chart
Micro vs Macro
Micro vs Macro
“Four Step” Model
What the macro model can do• Evaluate road widening and road additions• Evaluate new interchanges • Analyze the impacts of transportation plans • It can show impacts of large developments • It can forecast corridor volumes• It can be used as a basis for micro • It can test alternative land use plans
Macro model can not do well
• Evaluate new turn lanes at intersection (micro) • Model small or local roads very well (micro)
Are travel demand models perfect?
NO!
… but, it isTHE BEST DECISION MAKING TOOL CURRENTLY AVAILABLE FOR REGIONAL TRAVEL DEMAND
FORECASTING
Why are travel demand models not perfect?
• Merely a statistical replication of human behavior that assumes…– everyone acts rationally– demographic forecasts are reasonable– existing conditions are accurately reflected– external factors are known and under our control
Land Use Overview
Project No‐Project
Market Areas
Achievable Development
Achievable Development is an estimate of the reasonably expected intensity of development that is anticipated for a particular land use or parcel given known opportunities, constraints, and assumptions.
Achievable Development
Achievable Development: Determining Capacity
• Pending applications • Expired commitments• Prior analysis/design • Adjacent land use • Aerial imagery and topography• Historically densities for similar project types• Historical densities given regulations
Achievable Development: Determining Capacity
• Restrictions to land division • Prior mapping • Other restrictions or limitations
Achievable Development: Other considerations
• Exclude Tahoe Basin• Placerville provides its own• Treat Camino/Pollock Pines as Rural Center• Assume Williamson Act is constant• Consider higher Multi‐Family densities• Use GP not zoning• Consider mixed‐use
2035 Projections: Housing
2035 Projections: Population
2035 Projections: Population
2035 Projections: Population
2035 Projections: Population
2035 Projections: Population
2035 Projections: Employment
• Related to new housing• Regional economic growth• Highway 50 commute• Already approved projects• Establish a jobs‐to‐household ratio
2035 Land Use Forecast: Housing
2035 Land Use: Considerations
• General Plan and State legislation• Historical trends • Proximity to infrastructure and site access• Project status • Growth patterns • Proximity to major corridors• Proximity to other uses and services
Questions and Answers
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